1. Field of the Invention
This invention relates to a method of automatically controlling a discrete system, and more particularly to a computer control method which provides redundancy management and degraded operating modes in the presence of faulty system components and system conditions while resolving conflicting operational requirements according to a defined priority schedule. A discrete system as used herein is a system in which the control elements are set to two or more discrete states, such as a two position on/off valve.
In certain applications, such as automating a flight engineer's function of controlling the pneumatics/air conditioning system of an aircraft, the primary problem is one of managing system resources to provide the best possible level of system performance for existing conditions. To do this, an automated system controller must select a configuration of controllable components which handles current internal and external conditions. Conflicting requirements must be resolved according to defined priorities for handling the various conditions present. In systems which possess redundant resources, degraded levels of performance should be provided until all redundancy is exhausted in the presence of multiple faults and/or abnormal conditions. Control of the system involves an element of overall system supervision which requires planning and anticipation of the total system response to reconfiguration actions in order to avoid oscillatory control or thrashing. The control outcome must be deterministic, and the implementation should be capable of efficient implementation in terms of computer size and time of execution.
2. Description of the Prior Art
Automated solutions to control problems of similar nature are normally attempted using one of two techniques. One conventional technique is to work out in advance explicit responses for all possible input conditions and program them into the logic or data tables. Another technique is to use artificial intelligence/expert systems or knowledge based systems.
There are a number of problems and disadvantages associated with these techniques. For conventional techniques, the number of possible combinations becomes excessively large as the number of inputs conditions and/or control elements increases. The embodiment of explicit responses may require excessive memory or search time. It may not be possible to test all possible cases. In addition, hard coded logic is very inflexible and may require complete reprogramming when system requirements are modified.
For artificial intelligence techniques, responses may be non-deterministic or difficult to predict in advance, making the system uncertifiable for airborne applications. It is usually impossible to test all possible responses. Special language and/or processors may be required. Excessive execution time and/or memory may be required because rules or requirements are expressed in "if . . . then . . ." form.